If anything,oil in the fuel lubricates the fuel pump and injectors???
Thats kind of my take too.
When Premix enters a carb'd motor it goes through the reeds and immediately hits the piston skirt as the piston begins to travel back toward TDC. Once the piston skirt has cleared the cyl skirt the premix hits the connecting rod, crank and bearings. As the piston approaches TDC the incoming premix hits the exposed cylinder and piston pin bearings. After ignition the piston heads back downward where the piston and rings utilize the oil film to form a barrier between the piston and cylinder. As the piston is traveling downward on the power stroke the premix travels through the transfer ports and heads up into the combustion chamber area above the piston.
Once the premix enters the cylinder above the piston it lubricates the cylinder wall above the piston ring. As the piston travels back up on the compression stroke the rings wipe the oil off the cylinder. The oil helps the rings seal and provides some lubrication for the cylinder and piston but only above the the transfer ports and higher.
On a CFI-2 motor, Premix enters the cylinder from the boost ports when the piston is headed to BDC. A small amount of premix hits the piston at the boost ports but nowhere else on the piston. Once the piston has reached BDC the premix is in the combustion chamber area above the piston and rings. At this point the cylinders above the rings are being lubricated by the premix. As the piston travels back up on the compression cycle the premix is wiped from the cylinder walls by the rings. At no time does premix lubricate the cylinder below the transfer ports. A very small amount of premix will lubricate the piston in the area of the boost port but this is relatively insignificant.
In summary. Premix in a CFI-2 motor lubricates only the cylinder and only above the transfer ports. The rings wipe some of this lubrication off as the piston travels up. The amount of lubrication the piston skirt and lower cylinder get from this premix is debatable and IMO offers minimal additional protection for the piston.